The present invention relates to radiation curable silicone vinyl ethers and methods for preparing silicone vinyl ethers. More particularly, the present invention relates to compositions containing vinyl ether functional silicones and to the preparation and use of silicone vinyl ethers which are curable by addition of photocleavable acids and exposure to actinic radiation.
Alkenyl ether functional organosilicon compounds have been described in the art. For example, U.S. Pat. No. 4,617,238 to Crivello discloses and claims a photopolymerizable composition comprising (a) an organopolysiloxane having at least one Si-bonded vinyloxy functional group of the formula H.sub.2 C.dbd.CH--O--G--, where G is alkylene (such as propylene) or alkylene interrupted by at least one divalent heteroredical selected from --O--, divalent phenylene, or substituted divalent phenylene, or combination of such heteroradicals, and (b) an onium salt catalyst. The '238 patent also describes a method wherein the vinyl ether group is introduced into the organopolysiloxane by addition (hydrosilylation) of compounds with an allyl and a vinyl ether group to an SiH group of the organopolysiloxane in the presence of a platinum catalyst. In the method of the '238 patent, only the allyl group is added to the SiH group while the vinyl ether group is preserved and thus only one vinyl ether group for each SiH group can be incorporated into the siloxane molecule at any given time.
U.S. Pat. No. 4,707,503 to Itoh et al. discloses unsaturated organopolysiloxanes containing at least two organosiloxane groups represented by the formula CH.sub.2 .dbd.CR.sup.2 --X--R.sup.1 --SiR.sup.3.sub.m O.sub.3-m/m wherein R1 is a divalent hydrocarbon group, R.sup.2 is a hydrogen atom or a methyl group, R.sup.3 is a substituted or unsubstituted monovalent hydrocarbon group, X is a group --O--(CH.sub.2).sub.2 S--, and m is a number of 0, 1, or 2.
U.S. Pat. No. 5,057,549 to Herzig et al. discloses alkenyloxy functional organosilicon compounds which contain at least one Si-bonded Y radical per molecule having the formula --(CH.sub.2).sub.2 --R.sup.2 --(A--R.sup.3).sub.z --O--CH.dbd.CH--CH.sub.2 --R.sup.4, wherein A denotes --O--, --S--, or --C(O)O--, R.sup.2 denotes a linear or branched alkylene radical having from 1 to 7 carbon atoms per radical or cycloalkylene radical having from 5 to 7 carbon atoms per radical, R.sup.3 denotes a linear or branched alkylene radical having from 2 to 4 carbon atoms per radical, which may be substituted by a hydroxyl group, methoxy group, ethoxy group, or trimethylsiloxy group, R.sup.4 denotes a hydrogen atom or an alkyl radical having from 1 to 4 carbon atoms per radical, and z has a value of 0, 1, or 2. The alkenyloxy-functional organopolysiloxanes can be crosslinked for example with ultraviolet light and can be used for preparing coatings. The '549 patent further discloses that the alkenyloxy functional organosilicon compounds are prepared by reacting compounds of the formula CH.sub.2 .dbd.CH--R.sup.2 --(AR.sup.3).sub.z --OCH.sub.2 --CH.dbd.CH--R.sup.4 with an organosilicon compound having at least one Si-bonded hydrogen atom in the presence of a hydrosilylation catalyst, followed by a second step which effects the transfer of the carbon-carbon double bond to the carbon bonds beside the ether oxygen.
European Patent Publication No. 0462389 teaches thermosetting organopolysiloxanes with oxyalkylene vinyl ether groups bonded by SiOC groups and the vinyl groups may be substituted by alkyl radicals. EPO '389 also teaches a method for the preparation of these compounds and their application as photochemically thermosetting polysiloxanes in encapsulating compounds, as non-stick coating compounds for flat carriers or as modified additives in compounds which can be thermoset radically, cationically or by UV or electron radiation.
Another vinyl ether functional silicone is described in U.S. Pat. No. 5,039,716 to Vara et al. which discloses alk-1-enyl ether silicates having the formula [X].sub.4-n Si[OR.sup.1 OCH.dbd.CH--R.sup.2 ].sub.n wherein X is a halogen or --OR wherein R is lower alkyl or a mixture of halogen and OR, a mixture of OR and hydrogen or a mixture of halogen and hydrogen, R.sup.1 contains from 1 to 8 carbon atoms and is alkylene, alkenylene, alkynylene, optionally alkoxylated with up to 20 units of ##STR1## wherein Y is hydrogen or methyl and R.sup.2 is each hydrogen or lower alkyl and n has a value of 1 to 4. The '716 patent also discloses a process for preparing vinyl ether silicates.
The methods described hereinabove which rely on competition between the vinyl ether group and other alkenyl groups on the same compound do not result in conversion of SiH to vinyl ether. In contrast, the method of the present invention results in the quantitative conversion of siloxanes to vinyl ether, the preferred radiation sensitive group.